Which of the following is a correct statement about diversification?

a. To be properly diversified you need over 100 different stocks.

b. When a stock is combined into a portfolio that is not perfectly correlated with the stock, the standard deviation of the new portfolio will decrease.

c. Diversifiable or company-specific risk is the only risk that matters to a rational investor.

d. There is no limit to the amount of risk that can be eliminated through diversification.